Heretofore, a carbon black is compounded into rubber as a filler, and the rubber is reinforced by the compounding of the carbon black to improve physical properties of rubber such as wear resistance, tensile strength and the like. In general, a carbon black having a high reinforcing property can be obtained by controlling a surface nature of the carbon black, but a light transmittance of toluene extract is lowered at the same time to increase a tar component adhered onto the surface of the carbon black and hence this tar component obstructs the reinforcing property inherent to the carbon black. Therefore, there is naturally a limit for improving the reinforcing property of the carbon black (see JP-A-2000-53883, JP-A-10-36703 and JP-A-9-40883).
Also, rubber compositions compounded with the carbon black having a high reinforcing property are excellent in the wear resistance and the like, so that they are suitable as a tread rubber for a tire. In recent years, however, the rubber composition used in the tread rubber is required to be excellent in the low heat buildup in addition to the wear resistance from a demand of reducing a fuel consumption of the tire. These two performances are usually conflicting with each other, so that the establishment thereof is made first possible by improving the filler such as carbon black or the like.